1. Field of the Invention
The present invention relates to a photoelectric conversion device, and particularly relates to a photoelectric conversion device including thin film semiconductor elements. In addition, the present invention relates to electronic devices using the photoelectric conversion devices.
2. Description of the Related Art
A number of photoelectric conversion devices used for detecting an electromagnetic wave are generally known, and for example, photoelectric conversion devices having sensitivity from ultraviolet rays to infrared rays are collectively referred to as optical sensors. Among them, an optical sensor having sensitivity in a visible light region with a wavelength of 400 to 700 nm is particularly referred to as a visible light sensor, and a large number of visible light sensors are used for devices which need illuminance adjustment, on/off control, or the like depending on human living environment.
In some display devices, ambient brightness of the display device is detected to adjust display luminance. This is because unnecessary electric power of the display device can be reduced by detecting ambient brightness by an optical sensor and obtaining appropriate display luminance. For example, examples of display devices which have an optical sensor for adjusting luminance include a mobile phone and a computer.
In addition, as well as the ambient brightness of the display device, luminance of the backlight of a display device, in particular, a liquid crystal display device is also detected by an optical sensor to adjust luminance of a display screen.
As an optical sensor, a circuit in which a photoelectric conversion element such as a photodiode or the like is used for a light sensing part, a current which flows through an photoelectric conversion element in accordance with the incident light is made to flow through a resistor element, and ambient brightness is detected using the output voltage obtained is known (For example, see Reference 1: Japanese Published Patent Application No. 2005-129909).